<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      body {
        height: 100vh;
        width: 100vw;
        display: flex;
        justify-content: center;
        align-items: center;
        background-color: #e8e8e8;
      }

      button {
        text-decoration: none;
        position: relative;
        border: none;
        font-size: 14px;
        font-family: inherit;
        cursor: pointer;
        color: #fff;
        width: 9em;
        height: 3em;
        line-height: 2em;
        text-align: center;
        background: linear-gradient(90deg, #03a9f4, #f441a5, #ffeb3b, #03a9f4);
        background-size: 300%;
        border-radius: 30px;
        z-index: 1;
      }

      button:hover {
        animation: ani 8s linear infinite;
        border: none;
      }

      @keyframes ani {
        0% {
          background-position: 0%;
        }

        100% {
          background-position: 400%;
        }
      }

      button:before {
        content: "";
        position: absolute;
        top: -5px;
        left: -5px;
        right: -5px;
        bottom: -5px;
        z-index: -1;
        background: linear-gradient(90deg, #03a9f4, #f441a5, #ffeb3b, #03a9f4);
        background-size: 400%;
        border-radius: 35px;
        transition: 1s;
      }

      button:hover::before {
        filter: blur(20px);
      }

      button:active {
        background: linear-gradient(32deg, #03a9f4, #f441a5, #ffeb3b, #03a9f4);
      }
    </style>
  </head>
  <body>
    <button>Button</button>
  </body>
</html>
